Let’s go back two years ago when the Celtics owned the 25th pick and selected Providence scorer MarShon Brooks, then traded him to New Jersey for Johnson, who played 36 games as a rookie, was traded to Houston in the Courtney Lee deal, then was waived by the Rockets. He is currently out of the NBA.

Although Johnson aided the Celtics in netting Lee, they missed on players such as Chicago’s Jimmy Butler, Miami’s Norris Cole, and even Houston’s Chandler Parsons, a Rivers favorite who worked out for the Celtics twice and was convinced he was going to Boston.

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Of the 60 draft picks in 2011, Parsons has the fifth-highest scoring average despite falling to the 38th pick. The Celtics’ second-round selection in 2011, Johnson’s Purdue teammate, E’Twaun Moore, was also used in the Lee deal and is now flourishing with the Orlando Magic.

The Celtics had enough talent to miss in the draft and keep trucking. Rivers never really favored rookies anyway, he wouldn’t play them unless they were special — such as Glen Davis or Jared Sullinger — so taking chances in the draft was encouraged. Now? Not so much.

Boston needs to begin building cornerstones. Because their salaries are economical and they can be controlled for five years, first-round picks are valuable. The Celtics fought for a week with the Clippers, trying to pry a 2015 first-round pick for Rivers.

The Celtics select 16th in Thursday’s draft, their highest pick since the Big Three era began, and what’s different about this draft is 1) the Celtics won’t hesitate to take a player who can fill in for Paul Pierce or Kevin Garnett and, 2) this draft is so unpredictable they could end up with a lottery-caliber player.

My conversation with San Antonio general manager R.C. Buford at the NBA Finals regarding persevering as a franchise and also rebuilding one was eye-opening. The Celtics have to improve their approach in taking international players and also take the draft evaluation process more seriously.

Bill Walker, Gabe Pruitt, Melo, and Johnson are examples of the Celtics either taking wild chances or hoping a player with issues would develop in the Celtics’ system. Sullinger, projected as the No. 1 overall pick had he entered the draft following his freshman season at Ohio State, adjusted well last season.

Melo, meanwhile, was raw and there appears to be uncertainty about his future. While the Celtics have a pressing need at center, the organization has no idea whether Melo, the 22d overall pick last season, is capable of starting an NBA game.

Although acquiring Lee seemed to be a grand idea last summer, the Celtics sacrificed their second-round pick in the deal, meaning they will be inactive following the 16th pick unless they make a deal.

Second-round picks could also help the Celtics’ rebuilding effort if they can land a real prospect.

With Rivers gone, the chances of the Celtics attracting a premium free agent when they have loads of cap space in 2015 have lessened because they no longer have one of the league’s best recruiters. So that puts even more emphasis on the draft. Thursday night is important, even critical.

There are players who could be available, such as Shabazz Muhammad, Shane Larkin, Kelly Olynyk, or Dennis Schroeder. All bring starting NBA potential but also the chance of being a bust. Ainge said the club will take the best player available and in this case, that’s the most intelligent move.

The Celtics could use help at each position, given Jason Terry will be 36 when next season starts, Lee is perhaps an eighth man, and Avery Bradley doesn’t have a true position. With spirits drained after Rivers’s departure to the Los Angeles Clippers, Celtics fans need a reason for optimism.

They need to see a player who could step into the starting lineup, block a shot, grab rebounds, or soar to the basket for dunks.

They need to see a young player with cornerstone potential who could team with Rajon Rondo and Jeff Green to give the Celtics a capable trio, and one who could hypothetically learn from Pierce and Garnett for a season, then develop into a dependable player.

We haven’t seen those homegrown players around Boston much since the Big Three era began. The Celtics have produced a below-average draft score the past five years and the lack of younger players prepared to take over for Pierce and Garnett
is probably one of the factors that nudged Rivers to Los Angeles.

The post-Doc Rivers era has begun and as deflating as the past few days have been for Celtics fans, they could certainly use a shot of optimism with an impact draft pick.

Given the bizarre nature of this draft and the talent that could slide, it’s very possible.

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